This invention is directed to the fields of chimeric proteins and immunology.
Immunization against infectious disease has been one of the great achievements of modern medicine. Vaccines can be useful only if the vaccine, itself, is not significantly pathogenic. Many vaccines are produced by inactivating the pathogen. For example, hepatitis vaccines can be made by heating the virus and treating it with formaldehyde. Other vaccines, for example certain polio vaccines, are produced by attenuating a live pathogen. However, there is concern about producing attenuated vaccines for certain infectious agents whose pathology is not fully understood, such as HIV.
Molecular biology has enabled the production of subunit vaccines; vaccines in which the immunogen is a fragment or subunit of a parent protein or complex. Envelope proteins of HIV-1, such as gp120, are being evaluated as subunit vaccines. Several studies have suggested that antibodies to the V3 loop region of gp120 provide protection through virus neutralization. (Emini, E. A., et al., 1992, Nature 355, 728-30; Javaherian, K., et al., 1989, Proc Natl Acad Sci USA 86, 6768-72; Steimer, K. S., et. al., 1991, Science 254, 105-8; Wang, C. Y., et al., 1991, Science 254, 285-8.)
However, subunit vaccines may not be complex enough to generate an appropriate immune response. Also, when the pathogen is highly mutable, as is HIV, subunit vaccines that elicit strain-specific immunity may not be effective in providing global protection. Furthermore, the injection of inactive virus or even the envelope protein itself has the potential to produce a mixture of neutralizing and so-called “enhancing” antibodies. (Toth, F. D., et al., 1994, Clin Exp Immunol 96, 389-94; Eaton, A. M., et al., 1994, Aids Res Hum Retroviruses 10, 13-8; Mitchell, W. M., et al., 1995, Aids 9, 27-34; Montefiori, D. C., et al., 1996, J Infect Dis 173, 60-7.)
The immunogenicity of subunit vaccines is sometimes increased by coupling the subunit to a carrier protein to create a conjugate vaccine. One such carrier protein is Pseudomonas exotoxin A (“PE”). Investigators covalently linked a non-immunogenic O-polysaccharide derived from lipopolysaccharide (“LPS”) to PE. The resulting conjugate vaccine elicited an immune response against both LPS and PE. (S. J. Cryz, Jr. et al. (1987) J. Clin. Invest., 80:51-56 and S. J. Cryz, Jr. et al. (1990) J. Infectious Diseases, 163:1040-1045.) In another study, investigators were able to evoke an immune response against a Plasmodium falciparum antigen by coupling it through a spacer to PE. (J. U. Que et al. (1988) Infection and Immunity, 56:2645-49.) In a third study, investigators detoxified PE and chemically cross-linked it with principle neutralizing domain (“PND”) peptides of HIV-1. The conjugate vaccine elicited the production of antibodies that recognized PND peptide and neutralized the homologous strain, HIV-1MN. (S. J. Cryz, Jr. et al. (1995) Vaccine, 13:66-71.)
Chimeric proteins containing components of HIV-1 have been constructed and their immunogenic properties evaluated. These include: a poliovirus antigen containing an epitope of the gp41 transmembrane glycoprotein from HIV-1 (Evans, D. J., et al., 1989, Nature 339, 385-8), a mucit protein containing multiple copies of the V3 loop (Fontenot, J. D., et al., 1995, Proc Natl Acad Sci USA, 92, 315-9) a genetically modified cholera B chain with V3 loop sequences (Backstrom, M., et. al., 1994, Gene 149, 211-7) and a chemically detoxified PE-V3 loop peptide conjugate (Cryz, S., Jr., et al., 1995, Vaccine 13, 67-71).
The third variable (V3) loop of the envelope protein, gp120, contains the principal neutralizing domain of HIV-1. (Emini, E. A., et al., 1992, Nature 355, 728-30; Javaherian, K., et al., 1989, Proc Natl Acad Sci USA 86, 6768-72; Rusche, J. R., et al., [published errata appear in Proc Natl Acad Sci USA 22, 8697 1988, and Proc Natl Acad Sci USA 5, 1667 1989,]; Proc Natl Acad Sci USA 85, 3198-202 1988.) Although V3 loops vary considerably amongst the various HIV-1 strains (Berman, P. W., et al., 1990, Nature 345, 622-5) specific antibodies to this region have been shown to neutralize infectivity of the virus and to prevent viral cell fusion in vitro (Kovacs, J. A., et al. 1993, J. Clin Invest 92, 919-28). Further, systemic immunization with a recombinant form of gp120 appears sufficient to protect chimpanzees from infection by HIV-1 systemic challenge. White-Scharf, M. E., et al., 1993, Virology 192, 197-206.
HIV frequently gains entry to the body at mucosal surfaces. However, presently available HIV immunogens are not known to elicit a secretory immune response, which would inhibit viral access through the mucosa.
The development of a stable vaccine that could elicit both humoral and cellular responses, including mucosal immunity, and be flexible enough to incorporate sequences from many strains of an infectious agent, such as HIV-1, would be desirable.